Noise filling concept

Abstract

Noise filling of a spectrum of an audio signal is improved in quality with respect to the noise filled spectrum so that the reproduction of the noise filled audio signal is less annoying, by performing the noise filling in a manner dependent on a tonality of the audio signal.

The invention claimed is: 
     
       1. Apparatus configured to perform noise filling on a spectrum of an audio signal in a manner dependent on a tonality of the audio signal, wherein the apparatus is configured to:
 dequantize the spectrum, as derived after the noise-filling, using a spectrally varying and signal-adaptive quantization step size controlled via a linear prediction spectral envelope signaled via linear prediction coefficients in a data stream into which the spectrum is coded, or scale factors relating to scale factor bands, signaled in the data stream into which the spectrum is coded, 
 identify contiguous spectral zero-portions of the audio signal's spectrum and to apply the noise filling onto the contiguous spectral zero-portions identified, and 
 respectively fill the contiguous spectral zero-portions of the audio signal's spectrum with noise spectrally shaped with a function having a local maximum surrounded by two outwardly falling flanks wherein the function is set dependent on a respective contiguous spectral zero-portion's width so that the function is confined to the respective contiguous spectral zero-portion, and wherein a fill width at half maximum of the function is adjusted dependent on the tonality of the audio signal so that, if the tonality of the audio signal increases, the fill width at half maximum of the function gets more compact in an inner of the respective contiguous spectral zero-portion and distanced from the respective contiguous spectral zero-portion's outer edges. 
 
     
     
       2. Apparatus according to  claim 1 , wherein the apparatus is configured to scale the noise with which the contiguous spectral zero-portions are filled using a scalar global noise level signaled in the data stream into which the spectrum is coded in a spectrally global manner. 
     
     
       3. Apparatus according to  claim 1 , wherein the apparatus is configured to generate the noise with which the contiguous spectral zero-portions are filled, using a random or pseudo-random process or using patching. 
     
     
       4. Apparatus according to  claim 1 , wherein the apparatus is configured to derive the tonality from a coding parameter coded within the data stream so that the dependency on the tonality involves a dependency on the coding parameter. 
     
     
       5. Apparatus according to  claim 4 , wherein the apparatus is configured such that the coding parameter is one of
 an LTP (long-term prediction) flag or gain, and 
 a TNS (temporal noise shaping) enablement flag or gain, and 
 a spectrum rearrangement enablement flag signalling a coding option according to which quantized spectral values are spectrally re-arranged with additionally transmitting within the data stream the rearrangement prescription. 
 
     
     
       6. Apparatus according to  claim 1 , wherein the apparatus is configured to confine the performance of the noise filling onto a high-frequency spectral portion of the audio signal's spectrum. 
     
     
       7. Apparatus according to  claim 1 , wherein the apparatus is configured to set a low-frequency starting position of the high-frequency spectral portion corresponding to an explicit signaling in the data stream. 
     
     
       8. Apparatus according to  claim 1 , wherein the apparatus is configured to, in performing the noise filling, fill contiguous spectral zero-portions of the spectrum with noise a level of which exhibits a decrease from low to high frequencies, approximating a spectral low-pass filter's transfer function so as to counteract a spectral tilt caused by a pre-emphasis used to code the audio signal's spectrum. 
     
     
       9. Apparatus according to  claim 8 , wherein the apparatus is configured to adapt a steepness of the decrease to a pre-emphasis factor of the pre-emphasis. 
     
     
       10. Audio decoder supporting noise filling comprising an apparatus according to  claim 1 . 
     
     
       11. Perceptual transform audio decoder comprising
 an apparatus configured to perform noise filling on a spectrum of an audio signal according to  claim 1 ; and 
 a frequency domain noise shaper configured to subject the noise filled spectrum to spectral shaping using a spectral perceptual weighting function. 
 
     
     
       12. Audio encoder supporting noise filling comprising an apparatus according to  claim 1 , the encoder being configured to use a spectrum filled with noise by the apparatus, for analysis-by-synthesis. 
     
     
       13. Apparatus comprising a microprocessor configured to, an electronic circuit configured to, or a programmable computer programmed to:
 perform noise filling on a spectrum of an audio signal in a manner dependent on a tonality of the audio signal by filling a contiguous spectral zero-portion of the audio signal's spectrum with noise spectrally shaped by
 a function having a local maximum surrounded by two outwardly falling flanks wherein the function is set dependent on a respective contiguous spectral zero-portion's width so that the function is confined to the respective contiguous spectral zero-portion, and wherein a fill width at half maximum of the function is adjusted dependent on the tonality of the audio signal so that, if the tonality of the audio signal increases, the fill width at half maximum of the function gets more compact in an inner of the respective contiguous spectral zero-portion and distanced from the respective contiguous spectral zero-portion's outer edges, and 
 
 dequantize the spectrum, as derived by the noise-filling, using
 a spectrally varying and signal-adaptive quantization step size controlled via a linear prediction spectral envelope signaled via linear prediction coefficients in a data stream into which the spectrum is coded, or 
 scale factors relating to scale factor bands, signaled in the data stream into which the spectrum is coded.